Media enclosures providing reduced air gap around disk drive media surfaces of a disk drive

ABSTRACT

The inventors have discovered that aerodynamic forces contribute to disk fluttering. If the flow of air about these disk surfaces is unstable, the resulting aerodynamic forces can mechanically excite the disk surfaces, causing fluttering. The invention includes media enclosures constraining such aerodynamic effects, methods of making disk drives with these enclosures, the disk drives. This includes disk drives of at most 13 millimeters in height.

TECHNICAL FIELD

[0001] This invention relates to enclosures in a disk drive providing areduced air gap around disk drive media surfaces within the enclosure.

BACKGROUND ART

[0002] Disk drives are an important data storage technology, whichinclude several crucial components. Disk drive read-write heads directlycommunicate with a disk surface containing the data storage medium overa track on the disk surface. This invention involves improving theability to position at least one read-write head over the track on thedisk surface.

[0003]FIG. 1A illustrates a typical prior art high capacity disk drive10 including actuator arm 30 with voice coil 32, actuator axis 40,suspension or head arms 50-58 with slider/head unit 60 placed among thedisks 12.

[0004]FIG. 1B illustrates a typical prior art high capacity disk drive10 with actuator 20 including actuator arm 30 with voice coil 32,actuator axis 40, head arms 50-56 and slider/head units 60-66 with allbut one disk 12 removed as well as including spindle motor 80.

[0005] Since the 1980's, high capacity disk drives 10 have used voicecoil actuators 20-66 to position their read-write heads over specifictracks. The heads are mounted on head sliders 60-66, which float a smalldistance off the disk drive surface when in operation. Often there isone head per head slider for a given disk drive surface. There areusually multiple heads in a single disk drive, but for economic reasons,usually only one voice coil actuator.

[0006] Voice coil actuators are further composed of a fixed magnetactuator 20 interacting with a time varying electromagnetic fieldinduced by voice coil 32 to provide a lever action via actuator axis 40.The lever action acts to move head arms 50-56 positioning head sliderunits 60-66 over specific tracks with speed and accuracy. Actuator arms30 are often considered to include voice coil 32, actuator axis 40, headarms 50-56 and head sliders 60-66. Note that actuator arms 30 may haveas few as a single head arm 50. Note also that a single head arm 52 mayconnect with two head sliders 62 and 64.

[0007] Today, read-write head positioning errors are a significant pointof failure and performance degradation. These positioning errors arecaused in part by disk fluttering. Some fluttering problems for diskscan be attributed to instabilities in the motor turning the disk, whichare being addressed by the motor manufacturers.

[0008] The disk drive industry faces some significant challenges. Aseither recording densities or spindle speed increases, both headpositioning accuracy and head-flying stability must increase. Note thatcompetitiveness in the disk drive industry requires both requires bothincreased recording density and increased spindle speeds. Note thathead-flying is the motion of the read-write head over the disk surface,which flies a short distance off that surface.

[0009] In order to achieve an even higher track density essential formeeting the higher recording density requirements, the allowableposition error of the heads relative to registered data tracks isrequired to be less than 0.05 μm for the next few years.

[0010] New ways to improve head positioning and stabilize head-flyingare needed to meet these challenges, as well as improve the reliabilityof existing disk drives.

SUMMARY OF THE INVENTION

[0011] The inventors have found that the above needs can be achievedthrough further reduction of disk fluttering and flow-induced vibrationaround actuator arms. High-speed rotation results in large amplitudevibration of the head-slider suspension and the arms. Thus the reductionof flow-induced vibration is essential to current and future disk driveto protect head-positioning failures.

[0012] Aerodynamics has been an area of active and continuing researchsince at least the nineteenth century. Prandtl defined boundary layersearly in the twentieth century. The boundary layer concept was directlyapplicable to fluid flows involving air, water and other low viscosityfluids. The boundary layer is a fluid region near a surface withessentially no relative velocity with regards to that surface. Thisregion is caused by the effect of friction between the solid surface andthe fluid. The depth of this region is roughly proportional to thesquare root of the viscosity divided by the angular velocity of thesurface.

[0013] The inventors have discovered that aerodynamic forces contributeto disk fluttering. If the air flow around these disk surfaces isunstable, the resulting aerodynamic forces can mechanically excite thedisk surfaces, causing fluttering.

[0014] These aerodynamic forces act upon disk surfaces with respect tothe air cavity in which the disk surfaces rotate. A rotating disksurface will tend to create a rotating boundary layer of air. Thisboundary layer will tend to rotate in parallel to the motion of the disksurface. The stationary surface of the disk drive cavity facing the disksurface will also tend to generate a boundary layer. The inventorsdiscovered that when there is enough distance between the stationarysurface and the disk surface for more than the boundary layer of therotating disk surface, there is a back flow created against thedirection of flow from the rotating disk surface.

[0015] The inventors have discovered that a significant reduction indisk surface mechanical fluttering results from reducing the air gapbetween stationary surfaces facing the disk surface to about theboundary layer thickness. The inventors have found that when the airgaps are approximately the boundary layer thickness, there is improvedhead positioning. When the air gaps are smaller fractions of theboundary layer thickness, there are further improvements in headpositioning. These improvements are summarized for an operationalrotating velocity of 5400 Revolutions Per Minute (RPM) in FIG. 3.Similar improvements are expected for other operating rotationalvelocities such as 7200 RPM, 10,000 RPM and over 14,000 RPM.

[0016] The invention includes not only the mechanical enclosures housingdisk surfaces within a disk drive, but also the manufacturing methods,and the resulting disk drives. The disk drives may further be at most 13millimeters in height.

[0017] These and other advantages of the present invention will becomeapparent upon reading the following detailed descriptions and studyingthe various figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1A illustrates a typical prior art high capacity disk drive10 including actuator arm 30 with voice coil 32, actuator axis 40,suspension or head arms 50-58 with slider/head unit 60 placed among thedisks 12;

[0019]FIG. 1B illustrates a typical prior art high capacity disk drive10 with actuator 20 including actuator arm 30 with voice coil 32,actuator axis 40, head arms 50-56 and slider/head units 60-66 with allbut one disk 12 removed as well as including spindle motor 80;

[0020]FIG. 2A illustrates a cross section view of spindle motor 80 andone disk 12 with air flow between the upper disk surface 12 and top diskcavity face, as well as air flow between the lower disk surface 12 andbottom disk cavity face;

[0021]FIG. 2B illustrates the air flow situation between the upper disksurface 12 and top disk cavity face of FIG. 2A showing the formation oftwo separate boundary layers;

[0022]FIG. 2C illustrates the air flow situation between the lower disksurface 12 and bottom disk cavity face of FIG. 2A showing the formationof only one boundary layer;

[0023]FIG. 3 illustrates the relationship between the gap measured inmillimeters along the horizontal axis and head positioning errors as afunction of the gap for a disk surface rotating at 5400 RPM;

[0024]FIG. 4 illustrates an exploded schematic view of a thin disk drive10 using a single head and supporting various aspects of the invention;

[0025]FIG. 5 illustrates a top schematic view of the thin disk drive 10using the single head as illustrated in FIG. 4;

[0026]FIG. 6A illustrates a perspective view of voice coil actuatorcomponents 32, 40, 50, and 60, assembled with respect to the disk drivebase 110 as illustrated in FIGS. 4 and 5; and

[0027]FIG. 6B illustrates a perspective view the assembled disk base100, spindle motor 80, disk 12, disk clamp 82, and disk drive cover 110,of FIGS. 4 and 5.

DETAILED DESCRIPTION OF THE INVENTION

[0028]FIG. 2A illustrates a cross section view of spindle motor 80 andone disk 12 with air flow between the upper disk surface 12 and top diskcavity face, as well as air flow between the lower disk surface 12 andbottom disk cavity face.

[0029] A qualitative description of air flow about a disk surface 12 isas follows. Because of the no-slip condition, fluid in contact with thesurface rotates with the same angular velocity as the surface andexperiences the same centripetal acceleration. At the start of motion, aboundary layer begins to form in the circumferential direction. Fluid inthe boundary layer begins to spin but cannot maintain the samecentripetal acceleration as the surface. It acquires an outward radialcomponent. As the radial component increases in magnitude, a secondarylayer develops in the radial direction with stresses centrally directed.These stresses exert an excitation force on rotating disk leading to thedisk fluttering which impairs head-flying over that disk surface.

[0030]FIG. 2B illustrates the air flow situation between the upper disksurface 12 and top disk cavity face of FIG. 2A showing the formation oftwo separate boundary layers.

[0031] In a conventional hard disk drive, the flow pattern has secondaryflows, radially outward near the disk and inward at the housing, whichdominate the air flow. They are connected by axial flows near theperiphery and near the axle. When the gap between disk and cover/base iseven larger than that of boundary layer thickness, a significantquantity of fluid in the interior region is essentially isolated fromthe main flow. It rotates approximately as a rigid body at one-half theangular velocity of the disk. These flow characteristics make largevortex and accelerate disk-tilting effect, which results in a severePosition Error Signal (PES) problem.

[0032] It should be noted that in situations involving radial surfacemotion, the boundary layer is often formulated as proportional to thesquare root of the viscosity divided by radial velocity in radians persec. Table 1 illustrates the boundary layer thickness to Revolutions PerMinute (RPM). RPM Boundary Layer Thickness (mm) 5400 0.7 7200 0.5510,000 0.45

[0033]FIG. 2B reveals a large vortex over the area of the top disk of adisk stack, which may have just one disk. This vortex provides amechanical force acting to excite disk fluttering. This is the situationfound in all hard disk drives the inventors are aware of.

[0034] The inventors found that removing this large vortex in the areaof top disk reduces mechanical instability.

[0035] Near the rotating disk surface, toward its rim, air flowvelocities close nearing 20 meters (m) per second (sec) have been foundin simulations based on 5400 RPM. At the edge of the boundary layer,about one boundary layer thickness from the disk surface, air velocityis about 0. Further from the disk surface, a back flow forms due to thefriction with the stationary surface.

[0036]FIG. 2C illustrates the air flow situation between the lower disksurface 12 and bottom disk cavity face of FIG. 2A showing the formationof only one boundary layer.

[0037] By making the gap too narrow for secondary flows to exist asillustrated in FIG. 2C, the fluid adopts a Couette flow pattern with anearly straight-line, tangential velocity profile between the housingand the disk.

[0038]FIG. 3 illustrates the relationship between the gap measured inmillimeters along the horizontal axis and head positioning errors as afunction of the gap for a disk surface rotating at 5400 RPM.

[0039] The vertical axis is a percentage scale, with 100% being thecurrent head position error rates with contemporary gaps of about 1.2mm.

[0040] When the gap is made less than the boundary layer thickness of0.7 mm, errors in head positioning are about 75% compared toconventional error rates. Note that when the gap is about 0.4 mm, thehead positioning errors are 50% of conventional rates.

[0041] FIGS. 4 to 6B illustrate various schematic views a thin diskdrive 10 using a single head and supporting various aspects of theinvention.

[0042] Note that a thin disk drive may be preferred in certainapplications, such as multi-media entertainment centers and set-topboxes. Note that the thin disk drive using only a single head mayfurther be preferred, allowing further reduction in the gap between thebase 100 and the disk surface 12. The use of a single head in the thindisk drive aids in reducing manufacturing costs and increasingmanufacturing reliability.

[0043]FIG. 4 illustrates an exploded schematic view of a thin disk drive10 using a single head and supporting various aspects of the invention.

[0044] Disk drive 10 includes a printed circuit board assembly 120, adisk drive base 100, a spindle motor 80, a disk 12, a voice coilactuator 30, a disk clamp 82 and a disk drive cover 110. Voice coilactuator 30 may further include a single read-write head on ahead/slider 60. Disk drive cover 110 may further include at least oneregion 112 providing a top stationary surface close to disk 12 uppersurface.

[0045]FIG. 5 illustrates a top schematic view of the thin disk drive 10using the single head as illustrated in FIG. 4.

[0046] Note that region 112 may be essentially outside the regiontraveled by the actuator arm(s) 50 and head sliders 60 of voice coilactuator 30 when assembled and in normal operation.

[0047]FIG. 6A illustrates a perspective view of voice coil actuatorcomponents 32, 40, 50, and 60, assembled with respect to the disk drivebase 110 as illustrated in FIGS. 4 and 5.

[0048]FIG. 6B illustrates a perspective view the assembled disk base100, spindle motor 80, disk 12, disk clamp 82, and disk drive cover 110,of FIGS. 4 and 5.

[0049] The preceding embodiments have been provided by way of exampleand are not meant to constrain the scope of the following claims.

1. A disk drive, comprising: a disk drive cover including an top surfaceseparated from an upper disk surface of said disk drive by essentially afirst gap; and a disk drive base including a bottom surface separatedfrom a lower disk surface of said disk drive by essentially a secondgap; a disk containing at least one member of a disk surface collectioncomprising said upper disk surface and said lower disk surface; whereinall of said disk surface collection members rotate at an operatingrotational velocity; wherein rotation of said disk surface collectionmember at said operating rotational velocity creates a boundary layerthickness from said disk surface collection members, for each of saiddisk surface collection members; and wherein said disk drive coverfurther includes a second top surface region formed to facilitate themotion of an actuator arm between said disk cover and said upper disksurface; wherein said operating rotational velocity is at least 5400revolutions per minute; wherein a member of a gap collection is at mostsaid boundary layer thickness; wherein said gap collection is comprisedof said first gap and said second gap; wherein said disk drive has aheight of at most 13 millimeters.
 2. The apparatus of claim 1, whereinsaid disk drive base further includes a second bottom surface formed tofacilitate the motion of an actuator arm between said disk drive baseand said lower disk surface.
 3. The apparatus of claim 1, wherein saidoperating rotational velocity is at least 7200 revolutions per minute.4. The apparatus of claim 3, wherein said operating rotational velocityis at least 10,000 revolutions per minute.
 5. The apparatus of claim 4,wherein said operating rotational velocity is at least 14,000revolutions per minute.
 6. The apparatus of claim 1, wherein said gapcollection member is at most three quarters of said boundary layerthickness.
 7. The apparatus of claim 6, wherein said gap collectionmember is at most one half of said boundary layer thickness.
 8. Theapparatus of claim 7, wherein said gap collection member is at most onethird of said boundary layer thickness.
 9. The apparatus of claim 1,wherein said disk drive encloses at least two of said disks.
 10. Theapparatus of claim 1, wherein each of said gap collection members is atmost said boundary layer thickness.
 11. A media enclosure for a diskdrive, comprising: a disk drive cover including a top surface separatedfrom an upper disk surface of said disk drive by essentially a firstgap; and a disk drive base including a bottom surface separated from alower disk surface of said disk drive by essentially a second gap;wherein each member of a disk surface collection rotates at an operatingrotational velocity; wherein said disk surface collection is comprisedof said upper disk surface and said lower disk surface; wherein rotationof said disk surface collection member at said operating rotationalvelocity creates a boundary layer thickness from said disk surfacecollection member, for each of said disk surface collection members; andwherein said media enclosure encloses at least one disk of said diskdrive when assembled.
 12. The apparatus of claim 11, wherein said diskdrive cover further includes a second top surface region formed tofacilitate the motion of an actuator arm between said disk cover andsaid upper disk surface.
 13. The apparatus of claim 11, wherein saiddisk drive base further includes a second bottom surface formed tofacilitate the motion of an actuator arm between said disk drive baseand said lower disk surface.
 14. The apparatus of claim 11, wherein saidoperating rotational velocity is at least 5400 revolutions per minute.15. The apparatus of claim 14, wherein said operating rotationalvelocity is at least 7200 revolutions per minute.
 16. The apparatus ofclaim 15, wherein said operating rotational velocity is at least 10,000revolutions per minute.
 17. The apparatus of claim 16, wherein saidoperating rotational velocity is at least 14,000 revolutions per minute.18. The apparatus of claim 11, wherein at least one member of a gapcollection is at most said boundary layer thickness; wherein said gapcollection is comprised of said first gap and said second gap.
 19. Theapparatus of claim 18, wherein said gap collection member is at mostthree quarters of said boundary layer thickness.
 20. The apparatus ofclaim 19, wherein said gap collection member is at most one half of saidboundary layer thickness.
 21. The apparatus of claim 20, wherein saidgap collection member is at most one third of said boundary layerthickness.
 22. The apparatus of claim 11, wherein said media enclosureencloses exactly one disk of said disk drive.
 23. The apparatus of claim11, wherein said media enclosure encloses at least two disks of saiddisk drive
 24. The apparatus of claim 11, wherein each of said gapcollection members is at most said boundary layer thickness.
 25. Amethod of making a disk drive from said disk drive cover of claim 11 andfrom said disk drive base of claim 11, comprising the steps of: usingsaid disk drive cover to assemble said disk drive; and using said diskdrive base to assemble said disk drive.
 26. Said disk drive, as aproduct of the process of claim
 25. 27. Said disk drive of claim 26,wherein said disk drive has a height of at most 13 millimeters.